rust/src/patterns.rs

// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use Shape;
use codemap::SpanUtils;
use config::{IndentStyle, MultilineStyle};
use rewrite::{Rewrite, RewriteContext};
use utils::{wrap_str, format_mutability, mk_sp};
use lists::{DefinitiveListTactic, SeparatorTactic, format_item_list, itemize_list, ListItem,
            struct_lit_shape, struct_lit_tactic, shape_for_tactic, struct_lit_formatting,
            write_list};
use expr::{rewrite_unary_prefix, rewrite_pair};
use types::{rewrite_path, PathContext};
use super::Spanned;
use comment::FindUncommented;

use syntax::ast::{self, BindingMode, Pat, PatKind, FieldPat, RangeEnd};
use syntax::ptr;
use syntax::codemap::{self, BytePos, Span};

impl Rewrite for Pat {
    fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
        match self.node {
            PatKind::Box(ref pat) => rewrite_unary_prefix(context, "box ", &**pat, shape),
            PatKind::Ident(binding_mode, ident, ref sub_pat) => {
                let (prefix, mutability) = match binding_mode {
                    BindingMode::ByRef(mutability) => ("ref ", mutability),
                    BindingMode::ByValue(mutability) => ("", mutability),
                };
                let mut_infix = format_mutability(mutability);
                let id_str = ident.node.to_string();
                let sub_pat = match *sub_pat {
                    Some(ref p) => {
                        // 3 - ` @ `.
                        let width =
                            try_opt!(shape.width.checked_sub(prefix.len() + mut_infix.len() +
                                                             id_str.len() +
                                                             3));
                        format!(" @ {}",
                                try_opt!(p.rewrite(context, Shape::legacy(width, shape.indent))))
                    }
                    None => "".to_owned(),
                };

                let result = format!("{}{}{}{}", prefix, mut_infix, id_str, sub_pat);
                wrap_str(result, context.config.max_width(), shape)
            }
            PatKind::Wild => {
                if 1 <= shape.width {
                    Some("_".to_owned())
                } else {
                    None
                }
            }
            PatKind::Range(ref lhs, ref rhs, ref end_kind) => {
                match *end_kind {
                    RangeEnd::Included => {
                        rewrite_pair(&**lhs, &**rhs, "", "...", "", context, shape)
                    }
                    RangeEnd::Excluded => {
                        rewrite_pair(&**lhs, &**rhs, "", "..", "", context, shape)
                    }
                }
            }
            PatKind::Ref(ref pat, mutability) => {
                let prefix = format!("&{}", format_mutability(mutability));
                rewrite_unary_prefix(context, &prefix, &**pat, shape)
            }
            PatKind::Tuple(ref items, dotdot_pos) => {
                rewrite_tuple_pat(items, dotdot_pos, None, self.span, context, shape)
            }
            PatKind::Path(ref q_self, ref path) => {
                rewrite_path(context, PathContext::Expr, q_self.as_ref(), path, shape)
            }
            PatKind::TupleStruct(ref path, ref pat_vec, dotdot_pos) => {
                let path_str =
                    try_opt!(rewrite_path(context, PathContext::Expr, None, path, shape));
                rewrite_tuple_pat(pat_vec,
                                  dotdot_pos,
                                  Some(path_str),
                                  self.span,
                                  context,
                                  shape)
            }
            PatKind::Lit(ref expr) => expr.rewrite(context, shape),
            PatKind::Slice(ref prefix, ref slice_pat, ref suffix) => {
                // Rewrite all the sub-patterns.
                let prefix = prefix.iter().map(|p| p.rewrite(context, shape));
                let slice_pat =
                    slice_pat
                        .as_ref()
                        .map(|p| Some(format!("{}..", try_opt!(p.rewrite(context, shape)))));
                let suffix = suffix.iter().map(|p| p.rewrite(context, shape));

                // Munge them together.
                let pats: Option<Vec<String>> =
                    prefix.chain(slice_pat.into_iter()).chain(suffix).collect();

                // Check that all the rewrites succeeded, and if not return None.
                let pats = try_opt!(pats);

                // Unwrap all the sub-strings and join them with commas.
                let result = if context.config.spaces_within_square_brackets() {
                    format!("[ {} ]", pats.join(", "))
                } else {
                    format!("[{}]", pats.join(", "))
                };
                wrap_str(result, context.config.max_width(), shape)
            }
            PatKind::Struct(ref path, ref fields, elipses) => {
                rewrite_struct_pat(path, fields, elipses, self.span, context, shape)
            }
            // FIXME(#819) format pattern macros.
            PatKind::Mac(..) => {
                wrap_str(context.snippet(self.span),
                         context.config.max_width(),
                         shape)
            }
        }
    }
}

fn rewrite_struct_pat(path: &ast::Path,
                      fields: &[codemap::Spanned<ast::FieldPat>],
                      elipses: bool,
                      span: Span,
                      context: &RewriteContext,
                      shape: Shape)
                      -> Option<String> {
    // 2 =  ` {`
    let path_shape = try_opt!(shape.sub_width(2));
    let path_str = try_opt!(rewrite_path(context, PathContext::Expr, None, path, path_shape));

    if fields.len() == 0 && !elipses {
        return Some(format!("{} {{}}", path_str));
    }

    let (elipses_str, terminator) = if elipses { (", ..", "..") } else { ("", "}") };

    // 3 = ` { `, 2 = ` }`.
    let (h_shape, v_shape) =
        try_opt!(struct_lit_shape(shape, context, path_str.len() + 3, elipses_str.len() + 2));

    let items = itemize_list(context.codemap,
                             fields.iter(),
                             terminator,
                             |f| f.span.lo,
                             |f| f.span.hi,
                             |f| f.node.rewrite(context, v_shape),
                             context.codemap.span_after(span, "{"),
                             span.hi);
    let item_vec = items.collect::<Vec<_>>();

    let tactic = struct_lit_tactic(h_shape, context, &item_vec);
    let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
    let fmt = struct_lit_formatting(nested_shape, tactic, context, false);

    let mut fields_str = try_opt!(write_list(&item_vec, &fmt));

    if elipses {
        if fields_str.contains('\n') {
            // Add a missing trailing comma.
            if fmt.trailing_separator == SeparatorTactic::Never {
                fields_str.push_str(",");
            }
            fields_str.push_str("\n");
            fields_str.push_str(&nested_shape.indent.to_string(context.config));
            fields_str.push_str("..");
        } else {
            if !fields_str.is_empty() {
                // there are preceeding struct fields being matched on
                if fmt.tactic == DefinitiveListTactic::Vertical {
                    // if the tactic is Vertical, write_list already added a trailing ,
                    fields_str.push_str(" ");
                } else {
                    fields_str.push_str(", ");
                }
            }
            fields_str.push_str("..");
        }
    }


    let fields_str = if context.config.struct_lit_style() == IndentStyle::Block &&
                        (fields_str.contains('\n') ||
                         context.config.struct_lit_multiline_style() ==
                         MultilineStyle::ForceMulti ||
                         fields_str.len() > h_shape.map(|s| s.width).unwrap_or(0)) {
        format!("\n{}{}\n{}",
                v_shape.indent.to_string(context.config),
                fields_str,
                shape.indent.to_string(context.config))
    } else {
        // One liner or visual indent.
        format!(" {} ", fields_str)
    };

    Some(format!("{} {{{}}}", path_str, fields_str))
}

impl Rewrite for FieldPat {
    fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
        let pat = self.pat.rewrite(context, shape);
        if self.is_shorthand {
            pat
        } else {
            wrap_str(format!("{}: {}", self.ident.to_string(), try_opt!(pat)),
                     context.config.max_width(),
                     shape)
        }
    }
}

enum TuplePatField<'a> {
    Pat(&'a ptr::P<ast::Pat>),
    Dotdot(Span),
}

impl<'a> Rewrite for TuplePatField<'a> {
    fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
        match *self {
            TuplePatField::Pat(ref p) => p.rewrite(context, shape),
            TuplePatField::Dotdot(_) => Some("..".to_string()),
        }
    }
}

impl<'a> Spanned for TuplePatField<'a> {
    fn span(&self) -> Span {
        match *self {
            TuplePatField::Pat(ref p) => p.span(),
            TuplePatField::Dotdot(span) => span,
        }
    }
}

fn rewrite_tuple_pat(pats: &[ptr::P<ast::Pat>],
                     dotdot_pos: Option<usize>,
                     path_str: Option<String>,
                     span: Span,
                     context: &RewriteContext,
                     shape: Shape)
                     -> Option<String> {
    let mut pat_vec: Vec<_> = pats.into_iter().map(|x| TuplePatField::Pat(x)).collect();

    if let Some(pos) = dotdot_pos {
        let prev = if pos == 0 {
            span.lo
        } else {
            pats[pos - 1].span().hi
        };
        let next = if pos + 1 >= pats.len() {
            span.hi
        } else {
            pats[pos + 1].span().lo
        };
        let dot_span = mk_sp(prev, next);
        let snippet = context.snippet(dot_span);
        let lo = dot_span.lo + BytePos(snippet.find_uncommented("..").unwrap() as u32);
        let span = Span {
            lo: lo,
            // 2 == "..".len()
            hi: lo + BytePos(2),
            ctxt: codemap::NO_EXPANSION,
        };
        let dotdot = TuplePatField::Dotdot(span);
        pat_vec.insert(pos, dotdot);
    }

    if pat_vec.is_empty() {
        return Some(format!("{}()", try_opt!(path_str)));
    }
    // add comma if `(x,)`
    let add_comma = path_str.is_none() && pat_vec.len() == 1 && dotdot_pos.is_none();

    let path_len = path_str.as_ref().map(|p| p.len()).unwrap_or(0);
    // 2 = "()".len(), 3 = "(,)".len()
    let nested_shape = try_opt!(shape.sub_width(path_len + if add_comma { 3 } else { 2 }));
    // 1 = "(".len()
    let nested_shape = nested_shape.visual_indent(path_len + 1);
    let mut items: Vec<_> = itemize_list(context.codemap,
                                         pat_vec.iter(),
                                         if add_comma { ",)" } else { ")" },
                                         |item| item.span().lo,
                                         |item| item.span().hi,
                                         |item| item.rewrite(context, nested_shape),
                                         context.codemap.span_after(span, "("),
                                         span.hi - BytePos(1))
        .collect();

    // Condense wildcard string suffix into a single ..
    let wildcard_suffix_len = count_wildcard_suffix_len(&items);

    let list = if context.config.condense_wildcard_suffixes() && wildcard_suffix_len >= 2 {
        let new_item_count = 1 + pats.len() - wildcard_suffix_len;
        items[new_item_count - 1].item = Some("..".to_owned());

        let da_iter = items.into_iter().take(new_item_count);
        try_opt!(format_item_list(da_iter, nested_shape, context.config))
    } else {
        try_opt!(format_item_list(items.into_iter(), nested_shape, context.config))
    };

    match path_str {
        Some(path_str) => {
            Some(if context.config.spaces_within_parens() {
                     format!("{}( {} )", path_str, list)
                 } else {
                     format!("{}({})", path_str, list)
                 })
        }
        None => {
            let comma = if add_comma { "," } else { "" };
            Some(if context.config.spaces_within_parens() {
                     format!("( {}{} )", list, comma)
                 } else {
                     format!("({}{})", list, comma)
                 })
        }
    }
}

fn count_wildcard_suffix_len(items: &[ListItem]) -> usize {
    let mut suffix_len = 0;

    for item in items.iter().rev().take_while(|i| match i.item {
                                                  Some(ref internal_string) if internal_string ==
                                                                               "_" => true,
                                                  _ => false,
                                              }) {
        suffix_len += 1;

        if item.pre_comment.is_some() || item.post_comment.is_some() {
            break;
        }
    }

    suffix_len
}